1. Field of the Invention
The present invention relates generally to an inflatable passive restraint airbag module for restraining the movement of a seated occupant in a vehicle during impact and, more particularly, to an improvement in the canister and retainer, the method of assembly, and to the method for attaching the airbag module to the vehicle.
2. Description of Related Art
Safety restraint systems which self-activate without the need for intervention by an operator, i.e., “passive restraint systems,” typically are installed into a vehicle as an airbag module. The airbag module generally includes an inflatable cushion or airbag, an inflator, a canister, and a retainer to hold the airbag cushion and inflator within the canister. The canister provides structural support during inflation of the airbag and also provides a mounting base for installation of the airbag module in a vehicle. The canister is typically formed as an open mouth container with a center section and end plates fastened at each end by welds. During assembly of the canister, multiple specialized jigs as well as skilled operators are required to align the end caps properly on the center section for welding. If the end caps and center section are not aligned properly, the canister may not perform as desired during inflation because of deformation, thereby releasing the airbag or allowing gas leaks during inflation and preventing the airbag from being properly inflated. Complicating the circumstance is the fact that there are many brackets or fastening members welded to the center section to allow the airbag module to be secured within a vehicle. To provide the proper fit and finish when the airbag module is assembled into the vehicle, these fastening attachment members generally require special jigs and skilled operators to properly place them on the canister. Each jig used to assemble the canister is expensive and is typically unique to a particular canister and a particular vehicle, thus resulting in a significant amount of lost set-up time if a switch between vehicles or canisters is made.
Also typically used in airbag modules is a gas diffuser which diffuses the gas from the inflator, secured in a lower part of the canister, into the airbag, which is secured in the upper part of the canister. The diffuser helps proper gas flow into the airbag to ensure the desired inflation characteristics. The gas diffuser is typically secured to the canister by a retainer which also secures the airbag to the canister. During inflation the airbag applies a significant amount of stress and force to the canister and retainer and therefore each must be made out of a relatively thick sheet of metal which may limit tool life during formation of the canister, retainer, and diffuser. The gas diffuser and retainer being separate items also require additional assembly time to be properly assembled into the vehicle. The multiple attachment points that must also be attached to the vehicle require significant assembly time especially in aligning the canister for the proper fit and finish. The multiple fasteners and limited space available when the canister is assembled into the vehicle adds additional production steps and slows the assembly process, thereby increasing assembly cost.
Some manufacturers proposed snap tabs to assemble the end caps onto the center section of the canister. Typically these manufacturers use fastener assemblies such as bolts and nuts to ensure that the end caps are secured directly to the center section due to the stress experienced during deployment of the airbag. Other manufacturers proposed using the inflator which is bolted in place to further secure the end caps onto the canister. However, this latter approach raises additional problems. For example, and given the wide range of tolerances for the inflator, it is difficult to ensure that the end caps are properly secured and that they are not too loose or too tight. Improperly secured end caps may cause additional stress which may affect the performance of the canister during deployment of the airbag. Further, these snap tab attachments may be difficult to assemble properly with the proper alignment and generally do not perform during deployment of the airbag as well as welded assemblies.